1. Field of the Invention
The present invention relates to code conversion logic for a typewriter that produces a special tab code when a tab operation is keyboarded as a part of a text string that is being stored for subsequent playback.
2. Discussion Relative to the Art
Tabs are generally set by sequentially positioning the print point of a typewriter to a series of tab locations and at each location depressing the tab set key, thereby causing the respective tab locations to be stored in either a mechanical or an electronic storage. For playback of stored text strings, the tab code has typically caused the typewriter to perform as if the code was presently generated at the keyboard and the presently active tab settings are used. If the operator wishes to use the settings that were active when a document was originally keyboarded, as is usually the case, those settings must typically be restored by the operator prior to playback.
To avoid this inconvenience, provision has been made in some typewriters for storing the tab settings in a special data grouping preceding a stored text string. This approach has problems, however, if changes to the tab settings occur within the document as may be desireable when laying out a business form.
To permit greater flexibility, some typing systems associated with computer terminals permit a new set of tabs to be defined by inserting a tab set command in a text string.
A further approach to recording tab operations involves the conversion of the tab code to a corresponding series of space codes. With such an approach, however, additions or deletions that occur on a line ahead of a tab operation will shift the destination point of the tab operation a result that is generally not desired.
In typewriters that provide for automatic backspace/erase it is known to include in a text string a code to indicate the start point for a tab operation, such code being followed by a tab code. The start point information makes it possible to erase text in front of a tab without any need to reestablish correspondence between the reference point in storage and the print position. In this regard, it should be noted that on some typewriters, it is necessary to come forward from the beginning of the line to erase to the left of a tab on that line if correspondence is to be maintained between the print point and the reference point in storage.
For work with business forms, in particular, where tab settings may change a number of times for a single form, a more convenient approach for defining an operative set of tab positions would be desirable.